The present invention relates to semiconductor processing in general and to a method for determination of the internal orientation of a wafer in particular.
As known in the art, semiconductor chips are usually manufactured from dies of a semiconductor wafer. The dies are formed by a grid of perpendicular scribe lines that are oriented to certain crystallographic axes on the silicon substrate of the wafer. The silicon wafer will eventually be cut along the scribe lines into dies, which are the individual semiconductor chips obtained from the wafer. Wafer orientation is usually measured with the help of a marker on the wafer, such as a flat or a notch, which is oriented to certain crystallographic axes on the silicon substrate. It is very important to align the grid of scribe lines with the respect to the orientation axis of the wafer, i.e. the line connecting the notch center and the geometrical center of the wafer. It is also important to align the grid of scribe lines with the respect to geometrical center of the wafer.
FIG. 1 illustrates a silicon wafer, generally referenced 10. Typically a wafer has a orthogonal grid of scribe lines 12 generally, forming a plurality of dies, such as die 13. Scribe lines 12 intersect at junctions, for example, junction 14. Wafer 10 is generally circular but includes a notch 15 or a flat (not shown) that serves as an orientation marker.
Prior art methods for determining the coarse orientation of the wafer typically include the step of detecting by employing an optical sensor the position of the notch 15 or of the flat of the wafer while the wafer is rotated. Such a method is described in U.S. Pat. No. 6,038,312 assigned to the assignee of the present application and hereby incorporated by reference.
There is another common approach for wafer alignment in semiconductor manufacturing that recognizes the patterned features on a wafer. Such a method is described in U.S. Pat. Nos. 5,682,242 and 5,867,590 assigned to the assignee of the present application, both hereby incorporated by reference. The method determines the coarse directions of the grid lines relative to the direction of a reference coordinate system, and detects a direction of one of a plurality of directional features on the wafer, thereby providing a location of the grid junction in the reference coordinate system.
While the aforementioned patents provide methods for determining the location and orientation of distinguishing features of standard semiconductor wafers, it would nonetheless be of significant advantage to the semiconductor industry to be able to precisely determine other orienting parameters of the wafer, such as the orientation of the grid lines of the wafer relative to the wafer itself (i.e., the xe2x80x9cinternalxe2x80x9d orientation). It would also be of significant advantage to provide a method that enables locating the geometrical center of the wafer and of the wafer marker with an accuracy level that was previously unattainable.
It is therefore the primary object of the present invention to provide a method for determining the internal orientation of a wafer. It is also an object of the present invention to provide a method for determining the orientation of a wafer with increased accuracy. These and other objects of the present invention will become more apparent from the summary of the invention and detailed description of the drawings that follow.
There is a need in the art to facilitate inspection of the results of a photoresist exposure process, by providing a novel optical inspection method and system.
Generally speaking, there is a need for a technique capable of determining the internal orientation and location of a pattern on the surface of an object relative to the object itself.
Thus, the main idea of the present invention consists of determining of location of scribe lines relative to the geometrical center of the wafer and their orientation relative to the orientation axis of the wafer.
There is thus provided according to one broad aspect of the present invention a method for determining the orientation of a pattern on the surface of an object relative to the object, wherein the pattern comprises an array of generally perpendicular grid lines intersecting at grid junctions, and said object comprises a marker located at an edge thereof, the method comprising the steps of: determining the directions of the grid lines of the pattern relative to the direction of the reference coordinate system; determining the direction of object""s orientation axis relative to the direction of the reference coordinate system; determining the orientation of the grid lines relative to the object""s orientation axis; wherein said step of determining the orientation of the object""s orientation axis comprises the steps of determining a location of the geometrical center of the object in the reference coordinate system and detecting and determining a location of said marker in said reference coordinate system.
In accordance with a preferred embodiment of the present invention, the step of determining the orientation of the grid lines comprises detecting a pair of directional features thereby providing a location of the feature in the coordinate system.
Further in accordance with a preferred embodiment of the present invention, one of the directional features is located proximate to the geometrical center of the object and another is located proximate to the edge portion of the object.
Moreover in accordance with a preferred embodiment of the present invention, the directional features are of the same type.
Additionally in accordance with a preferred embodiment of the present invention, the directional features are of different types.
Thus, according to another broad aspect of the present invention, there is provided a method for a method for determining the location of a pattern on the surface of an object relative to the object, wherein the pattern comprises an array of generally perpendicular grid lines intersecting at grid junctions, and the object comprises a marker located at an edge thereof, the method comprising the steps of: determining the directions of the grid lines relative to the direction of the reference coordinate system; determining a location of the geometrical center of the object in said reference coordinate system; calculating the displacement of the grid lines relative to geometrical center of the object.
In accordance with a preferred embodiment of the present invention, the displacement of the grid lines is calculated as the displacement between the geometrical center of the object relative to one of four grid junctions located adjacent to said geometrical center.
Further in accordance with a preferred embodiment of the present invention, the step of determining the location of the geometrical center of the object comprises obtaining at least three imaging frames spaced along edge portions of the object, obtaining coordinates corresponding to the outer edge of the object within said at least three frames using image processing and computing the geometrical center of the object using said coordinates.
Still further in accordance with a preferred embodiment of the present invention, said at least three imaging frames are equally spaced along edge portions of the object.
Moreover in accordance with a preferred embodiment of the present invention, said image processing comprises the use of optical filtering.
Additionally in accordance with a preferred embodiment of the present invention, said filtering is Gaussian filtering.
Further in accordance with a preferred embodiment of the present invention, said filtering is Sobel filtering.
Still further in accordance with a preferred embodiment of the present invention, said image processing in the step of obtaining coordinates corresponding to the outer edge of the object within said at least three frames uses image processing initiated from the outside boundary of said frames.
Moreover in accordance with a preferred embodiment of the present invention, the method further comprises providing a substantially reflective background under the outer edge of the object.
Additionally in accordance with a preferred embodiment of the present invention, the method further comprises providing a substantially non-reflective background under the outer edge of the object.
Further in accordance with a preferred embodiment of the present invention, the step of determining a location of said marker in said reference coordinate system comprises determining a location of a center of curve approximating said marker.
Still further in accordance with a preferred embodiment of the present invention, said curve is a curve of even order.
Moreover in accordance with a preferred embodiment of the present invention, said curve is a circle.
Additionally in accordance with a preferred embodiment of the present invention, said curve is an ellipse.
Further in accordance with a preferred embodiment of the present invention, said curve is a parabola.
Still further in accordance with a preferred embodiment of the present invention, the step of detection of said marker comprises analyze of coordinates of three points located on the edge portion of the object.
Moreover in accordance with a preferred embodiment of the present invention, the method further comprises the step of pre-aligning the object with respect to a reference coordinate system.
Further in accordance with a preferred embodiment of the present invention, the step of pre-aligning the object comprises determining the location of a marker on an edge of the object and rotating the object such that said marker is held at a predetermined measurement location with respect to said reference coordinate system.
Still further in accordance with a preferred embodiment of the present invention, the object is a semiconductor wafer.
Moreover in accordance with a preferred embodiment of the present invention, the grid lines are scribe lines between dies of said semiconductor wafer.
Additionally in accordance with a preferred embodiment of the present invention, the marker is a notch.
Further in accordance with a preferred embodiment of the present invention, the marker is a flat.
Still further in accordance with a preferred embodiment of the present invention, the pattern on the surface of semiconductor wafer is formed by photoresist.
Moreover in accordance with a preferred embodiment of the present invention, the step of determining the orientation of a pattern on the surface of an object relative to the object is performed after performing photoresist developing for first patterned layer.